Cryo-preparation systems and methods for near-instantaneous vitrification of biological samples

ABSTRACT

A sample vitrification system includes a capsule structure configured for carrying a biological sample within a compartment while the sample is subjected to ultra-rapid freezing by way of a cryogenic coolant jet, and while the sample is exposed to pulsed microwave radiation in a manner that disrupts water molecule pentamer formation and which disrupts initial ice crystal nucleation events within the compartment within tens of microseconds to provide a vitrification depth within the compartment of tens of microns or more. The sample can reside between a very high thermal conductivity substrate and a cover. The cryogenic coolant jet is applied to the substrate from beneath the sample. The cover can carry a set of microwave excitation elements configured for providing microwave radiation to internal portions of the compartment. Portions of the capsule structure&#39;s interior can be imaged during microwave assisted jet freezing, such as by way of an optical microscope.

TECHNICAL FIELD

The present disclosure relates generally to techniques for selectivelyapplying microwave energy to biological samples in association withpreparing such samples for imaging, analysis, and/or processing. Moreparticularly, aspects of the present disclosure are directed to systems,apparatuses, devices, and processes for selectively applying microwaveand/or other energy to biological and/or other samples during samplevitrification procedures.

BACKGROUND

The study of biological specimens with charged particles remainsintegral to the advancement of the biological sciences owing to itssuperior resolution compared to optical techniques. However, suchsystems work in a vacuum environment so typically the specimens must bechemically altered and dehydrated prior to imaging. This presents anobstacle to obtaining reliable information because faithful imagingdepends critically on the sample preparation technique and alldehydration techniques produce artifacts (protein loss, shrinkage etc).

Imaging specimens in a pristine hydrated state (even in vacuum) ispossible if the sample is frozen, but care must be taken to avoid theformation of ice crystals which cause disruption of the cellularstructure. Typically, techniques currently employed attempt to decreasethe temperature of the specimen below the freezing point faster than icecrystals can propagate in the media (a cooling rate of approximately10,000 degrees Kelvin/sec is required), and thus a crystal-freeamorphous or “vitreous” region free of artifacts can be achieved.However, the range of environmental conditions under which vitrificationcan occur is extremely limited and current cryo-preparation techniqueshave major shortcomings. For example, in slam freezing, where the sampleis forced on a cold metal block (Liquid Nitrogen, LN, temperature orcolder), the vitreous region is limited to about 5 microns in depth.This is because of the limited thermal conductivity of the water in thesample. Often the features of interest exist deeper than this shallowvitreous region, and hence such features of interest are subject toextensive crystal damage. Moreover, even a thin layer of water on thesample surface can take up a significant fraction of this vitreousregion, providing limited or no information about the sample whatsoever.A much more effective approach is to freeze the samples under extremelyhigh pressures of approximately 2100 bar (i.e., about 30,000 psi), wherethe freezing temperature of water is depressed and the propagation speedof the crystal growth is significantly reduced due to viscosity changeswithin the material. High pressure freezing is currently a type of “goldstandard” for sample preparation, providing vitreous regions having adepth of up to approximately 200 microns within the sample.Unfortunately, high pressure freezers are undesirably expensive(approximately $250,000 USD), and they require delicate, time consumingsample preparation prior loading into the freezer.

As described in “An improved cryofixation method: cryoquenching of smalltissue blocks during microwave irradiation,” J. Microsc. 165, 255-271(1992), Hanyu et al. found that a vitreous region within a sampleundergoing slam freezing could be extended to 15 microns using amicrowave assisted slam freezing technique, in which continuous wave(CW) microwave energy was provided in a manner that disrupted theaggregation of water molecules which into pentamer structures (breakingthem into monomers) immediately before the onset of a freezing wave, asindicated in FIG. 1A. Hanyu found that microwave assisted disruption ofnucleation sites significantly extended the depth of vitrification, andalso changed the character of the ice crystals which formed beyond thevitrified zone. More particularly, as indicated in FIG. 1B, at depthsbeyond 15 microns, the crystals remained substantially smaller (boundedto less than 50 nm) than in the control-case without microwavedisruption (where the crystal size increased without bound beyond 5microns depth).

Hanyu's apparatus, which is shown in FIGS. 1C and 1D, exposed the sampleto microwave radiation as the sample underwent free-fall through awaveguide cavity. The exposure of Hanyu's sample to microwave radiationthus occurred during the time it took the sample to free-fall throughthe cavity, just prior to impinging on a LN cooled copper block disposedbeyond a lower border of the cavity. Unfortunately, Hanyu's apparatuswas undesirably limited with respect to the manner in which appliedmicrowave energy interacted with the propagation of a freezing wavewithin the sample. Furthermore, Hanyu's apparatus was quite cumbersomein terms of its size, configuration, and difficulty of integration withstandard microscopy systems or microscopes, and lack of scalability.Additionally, Hanyu's cooling head needed to be re-heated and polishedbetween each sample, so Hanyu's apparatus is not well suited tocorrelative microscopy.

A need exists for a system, apparatus, device and method that providesgreatly improved performance over slam or plunge freezing by way of theselective application of microwave energy to a sample during slamfreezing, which provides vitrification depths of up to tens of micronsor more, which can be readily integrated with standard types ofmicroscopy equipment (e.g., optical microscopes), which is well-suitedfor correlative microscopy, and which has a cost that is much lower thancurrent high pressure devices.

SUMMARY

Embodiments in accordance with the present disclosure provide systems,apparatuses, devices, and procedures for advancing the state-of-the-artof cryo-preparation by way of applying pulsed microwave energy (forinstance, between approximately 2.0-18 GHz, e.g., approximately 2.45GHz, 5.0 GHz, 5.8 GHz, 8.0 GHz, or 10 GHz; and/or another frequency) toa sample or specimen as it is very rapidly cooled in a manner thatsubstantially or essentially entirely avoids ice crystal formationwithin the sample, thereby managing, controlling, and/or increasing thedepth of vitrification within the sample. The timing and power densityof the microwave energy are provided in a manner that disrupts watermolecules which have aggregated into a pentamer structure (breaking theminto monomers) immediately before the onset of a freezing wave. Moreparticularly, various embodiments in accordance with the presentdisclosure are configured for the application of a microwave signalpulse train that includes multiple high power pulses, but which has lowaverage power, to the sample. Embodiments in accordance with the presentdisclosure can thus at least substantially minimize, avoid, or preventthe formation of ice crystals within portions of the sample.

Various embodiments in accordance with the present disclosure canprovide vitrification depths up to tens of microns or more, at a costthat is much lower (e.g., ten times lower) than current high pressuredevices, and can enable a near instantaneous freeze of the specimen(within tens of microseconds) after a key, trigger, or target event isinitialized, initiated, or observed. Embodiments in accordance with thepresent disclosure can be compact or highly compact, and can be readilyintegrated with or retrofitted onto existing instruments such as opticalmicroscopes, which along with charged particle systems are ubiquitous inuniversities and research institutions. Systems, apparatuses, anddevices in accordance with embodiments of the present disclosure arewell suited to and can thus greatly increase the utility of correlativemicroscopy. Consequently, embodiments in accordance with the presentdisclosure can become integral elements in the rapidly expanding fieldof correlative microscopy, which has an estimated annual marketexceeding approximately $70M USD for charged particle optics instrumentsin correlative biological applications, corresponding to roughly 200 ormore instruments per year.

FIG. 2A is a schematic illustrations showing particular portions of asample preparation, fixation, processing, observation, and/orexamination system 10 in accordance with an embodiment of the presentdisclosure. The system 10 includes a carrier or capsule structure 110configured for carrying, holding, or retaining one or more samples orspecimens (e.g., a sample disposed within or carried by a liquid) withina recess, chamber, or compartment 116 while the sample is subjected toultra-rapid freezing by way of exposure to a cryogenic coolant jet 220.The capsule structure 110 can include or be coupled to a very high orextremely high thermal conductivity substrate 112, such as a diamond orsapphire material, to facilitate extremely rapid thermal energytransfer; and a cover 114, such that the sample resides between thesubstrate 112 and the cover 114. Portions of the capsule structure 110can further be exposed to, support, carry, or include a set of microwaveenergy application or microwave signal delivery elements 122, which canprovide microwave signals to internal portions of the compartment 116,and hence to the sample, during an ultra-rapid or jet freezingprocedure. In some embodiments, one or more portions of thecompartment's interior can be viewed or imaged during freezing, such asby way of a microscope objective 55. The capsule structure 110 itselfcan be matingly or removably coupled to a panel, platform, or stagestructure, such as a microscope stage or platform. In a number ofembodiments, one or more portions of the capsule structure 110 can bedisposable. To understand aspects of the motivation underlyingparticular embodiments in accordance with the present disclosure, a moredetailed examination of sample or specimen cooling is required. FIG. 2Bis a schematic illustration of representative regions within a sample asthe sample undergoes ultra-rapid or jet freezing. In FIG. 2B, Region Icorresponds to a diamond substrate 112 which is at LN temperature;Region II corresponds to an initial vitrified frozen interface, which isdynamic and propagating; Region III corresponds to unfrozen, pre-cooledliquid in proximity to the frozen interface; Regions IV and V correspondto the remaining aqueous solution; and Region VI corresponds to thecover 114, through which the sample can be imaged.

Without microwave disruption, the cooling rate and the advance of thefrozen interface can be calculated with basic thermodynamic and heattransfer equations. Ideally, within the first 5 microns andapproximately 5 microseconds, the cooling rates (e.g., approximately10,000 K degrees/sec) are sufficient for vitrification. As timeprogresses, the low thermal conductivity of the sample in Region IIdegrates the cooling rate substantially. The pre-cooling exacerbates theproblem because the concentration of water pentamers increasesdramatically as the temperature is reduced. For example, at 298K waterconsists of approximately 85% pentamers (Ohtomo et al, 1982). Hanyu'sapproach disrupted the pentamers; however, the molecular relaxation timeis much faster than the propagation times of the cooling front(milliseconds), so the nucleation sites reform rapidly, particularly inpre-cooled Region III. Continuous-Wave (CW) application of microwaves isan option, but since the microwave absorption cannot be avoided inRegion IV, the power density must be limited to prevent sample heatingand degradation.

In FIG. 2B, the aqueous region has been partitioned, and the interfacebetween Regions IV and V (about 50 microns from the substrate)represents the plane at which more rapid cooling at the substrate 110 nolonger improves the cooling rate in Region V (as long as it is above athreshold of approximately 5K-10K degrees/sec). That is, even aninfinite cooling rate in Region I will not improve the cooling rate inRegion V because the thermal diffusion has become limited by the lowerdiffusivity of the vitrified sample. This is a consequence of thediffusion process, where the diffusion time depends upon distancesquared. One additional noteworthy property is that the thermaldiffusivity of the vitrified region is lower than that of water, so thepre-cooled region expands faster than the propagation of the vitrifiedinterface.

Various embodiments in accordance with the present disclosure areintended to overcome these limitations, so that much greater peak powerdensities can be employed at the critical interface the instant beforefreezing. Additionally, by controlling the duty factor, detrimentalthermal effects in Regions IV and V can be mitigated.

An appropriate choice of microwave irradiation frequency also protectsthe vitrified region of the sample (Region II) from inadvertent heatingand re-melting. Appropriate microwave excitation isolates a particularmode of energy transfer which involves only the rotation of themolecules around their dipole. This rotational excitation is extremelyeffective at breaking the pentamers. Once the molecules are frozen inthe vitreous region they lack the ability to rotate, and theirabsorption of microwave energy decreases by 3 to 4 orders of magnitude.This enables a more aggressive application of microwave peak power, asheating of the aqueous solution is limited only by the time averagedmicrowave power.

FIG. 2B is a graph indicating the imaginary part of the Index ofRefraction for water and ice relative to the frequency or wavelength ofapplied radiation. As can be seen in FIG. 2B, the efficiency ofmicrowave coupling to the water increases with frequency up to about 18GHz, agreeing well with the classic debye model for this dielectricsystem. Additionally, the dimensions of microwave applicators ormicrowave signal delivery elements decreases with higher frequency,providing for a more compact apparatus, suggesting operation near 18 GHzis desirable. However, these trends should be balanced relative to theavailability of low cost microwave power sources (e.g., WiFicomponents), and available license-free ISM (Industrial, Scientific, andMedical), frequency bands, three of which are shown in FIG. 2B (i.e.,2.45 GHz, 5.8 GHz, and 10 GHz). Multiple embodiments in accordance withthe present disclosure are configured for providing microwave sampleexcitation at approximately 5.8 or 10 GHz; however, other embodimentscan be configured for higher frequency excitation.

In various embodiments, the microwave pulse characteristics (e.g.,amplitude, pulse duration, and/or inter-pulse interval or period betweenpulses) are managed, controlled, tailored, or optimized to substantiallyor essentially match the velocity of the propagating freezing front andthe extent of the pre-cooled region, and are applied in a sequence thatis sufficiently rapid to disrupt nucleation events before they occur,become established, or propagate, for instance, by way of dendriticgrowth, which has been found by Stan et. al in “Apparatus for the Studyof Ice Nucleation in Supecooled Water Drops,” Lab Chip, 2009, 9,2293-2305, to be the first stage of ice crystal formation that isinitiated in supercooled water drops within tens of microseconds, andwhich is completed within 300 microseconds. Nonuniform dendritic growthis followed by a uniform freezing phase from outer edges of a sampletoward sample center, and lasts an additional tens of milliseconds. Invarious embodiments in accordance with the present disclosure, specimenor sample thickness can be up to approximately 200 microns, so afreezing process can last up to approximately 100 milliseconds.Embodiments in accordance with the present disclosure can apply pulsedmicrowave signals in a manner that substantially or effectively reduces,minimizes, or arrests initial nucleation events within tens ofmicroseconds. In certain embodiments, one or more of the aforementionedparameters can change during the progression of the freeze.

Prior ultra-rapid freezing techniques undesirably freeze a sample from atop exposed surface, either by slamming the specimen onto a polishedmetal block (e.g., slam freezing) or by plunging it into a cryocoolant.This presents many difficulties, of which the most pressing is therequirement to blot the aqueous solution from the surface prior to thefreeze. The blotting procedure can lead to inconsistent results, giventhat an aqueous film of only 5-10 microns would consume most or all of alimited vitrified region. It is also time-consuming, eliminating thepossibility of “freezing” rapid events. Approaches in accordance withembodiments of the present disclosure cool the sample underneath, thatis, from a substrate side, for instance, using a super-cooled propellantjet (liquid ethane at LN temperatures, or one or more othercryocoolants). This eliminates the problems of a water layer, allowingfor in-situ imaging immediately preceding, during, and after the freeze.Cells, bacteria, or other biological specimens carried by the substratecan remain submerged in a buffer layer such as an aqueous buffer, sincethe important information is tied directly to the substrate 112 andcrystal growth in the aqueous buffer is inconsequential. This alsoallows for studies which can lock-in a condition a few millisecondsafter an observed or triggering event.

Substrates 112 configured for carrying or thermally interfacing withsamples in accordance with embodiments of the present disclosure providea very high or extremely high thermal conductivity. Multiple embodimentsemploy thin re-usable optical grade diamond substrates, while otherembodiments can employ other types of substrates (e.g., sapphire).Diamond has the highest thermal conductivity of any material, farsurpassing that of copper, the best metallic conductor. The heattransfer mechanism of diamond is also fundamentally different than thatof metals, conducting heat through phonons rather than electrons, andprovides enhanced conductivity near LN temperatures. Optical diamondsubstrates are commercially available and relatively inexpensive (e.g.available at element six, www.e6cvd.com). Reuse of the substrates 112 ispossible with simple cleaning procedures between uses. The substrates112 are bio-compatible and can be configured with fiducial markers,either through metallized patterns or etching, so that specific regionsof interest can be identified trivially by the markers as the sampletransitions from optical to charged particle instruments.

A number of elements or components in accordance with embodiments of thepresent disclosure can be miniaturized to adapt to or fit in a standard,replaceable panel, platform, or stage on an optical microscope (e.g., anupright microscope configuration). In accordance with embodiments of thepresent disclosure, a set of microwave excitation or signal applicationelements is compact and does not significantly interfere with either anobjective lens above or a light illumination source below the samplechamber or capsule. Multiple types of microwave signal delivery elementscan be configured to apply microwave energy to a sample within a chamberin accordance with embodiments of the present disclosure, for instance,strip lines and a slab-line elements (e.g., which can be coupled tocoaxial cables).

Additionally, in various embodiments an appropriate cryocoolant deliverysystem design is utilized, which can substantially or essentiallyentirely avoid interference with an illumination source below thesample, and which remains in a non-contact mode prior to cooling (toprevent pre-cooling of the sample) during optical studies. The fluiddynamics as cryocoolant is ejected from a nozzle facilitate or assureminimal stagnation points and highly uniform cooling across relevantportions of the substrate back plane or the entire substrate back plane.Geometrical aspects of a substrate 112 can be configured in one or moremanners to provide an effective or maximum cooling rate, but withsufficient structural stability so that it does not warp the substrate112 as it is cooled. Several embodiments can empty substrates 112 havinga thickness of 0.5 mm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an illustration of a disruption of water molecule pentamerstructures into monomer structures.

FIG. 1B is a graph illustrating microwave assisted slam freezing resultsdescribed by Hanyu et al.

FIGS. 1C and 1D illustrate a microwave assisted slam freezing apparatusdescribed by Hanyu et al.

FIG. 2A is a schematic illustrations showing particular portions of asample preparation, fixation, processing, observation, and/orexamination system 10 in accordance with an embodiment of the presentdisclosure.

FIG. 2B is a schematic illustration of representative regions within asample as the sample undergoes ultra-rapid freezing.

FIG. 3A is a schematic illustration of a sample preparation, fixation,processing, observation, and/or examination system in accordance with anembodiment of the present disclosure.

FIG. 3B is a schematic illustration showing portions of a samplevitrification system in accordance with another embodiment of thepresent disclosure.

FIGS. 4A-4D are representative illustrations showing portions of samplechambers, receptacles, or capsules in accordance with particularembodiments of the present disclosure.

FIGS. 5A and 5B illustrate aspects of a cooling unit that can direct atleast one cryogenic coolant jet to a very high or extremely high thermalconductivity substrate in accordance with embodiments of the presentdisclosure.

FIGS. 6A-6H are schematic illustrations of a cryocoolant jet that isincident upon very high or extremely high thermal conductivitysubstrates having one or more patterned substrate regions in accordancewith embodiments of the present disclosure.

FIG. 7A is a schematic illustration of a microwave probe in accordancewith an embodiment of the present disclosure.

FIGS. 7B and 7C are schematic illustrations of a microwaveprobe/cryocoolant applicator in accordance with embodiments of thepresent disclosure.

FIGS. 8A-8D are schematic illustrations of a microstrip capsulestructure or assembly in accordance with an embodiment of the presentdisclosure.

FIGS. 8E-8G are schematic illustrations of a coplanar microstrip capsulestructure or assembly in accordance with an embodiment of the presentdisclosure.

FIG. 8H is a schematic illustration of a generalized microstrip capsulestructure or assembly in accordance with an embodiment of the presentdisclosure.

FIGS. 9A-9D are schematic illustrations of portions a microstrip-basedcapsule structure or assembly in accordance with yet another embodimentof the present disclosure.

FIG. 9E is a schematic illustration of a representative type of fractureinitiation element carried by a microstrip-based capsule structure orassembly in accordance with an embodiment of the present disclosure.

FIGS. 10A-10B schematic illustrations of further aspects of themicrostrip-based capsule structure of FIGS. 9A-9D in accordance with anembodiment of the disclosure.

FIGS. 10C-10I are illustrations showing particular aspects of themicrostrip-based capsule structure of FIGS. 9A-10B.

FIGS. 11A-11D are block diagrams showing aspects of a design formicrowave signal generation and delivery circuitry in accordance with anembodiment of the present disclosure.

FIG. 11E is an image showing portions of a representative prototypesample preparation or fixation system in accordance with an embodimentof the present disclosure.

FIGS. 12A and 12B are images of a particular type of commerciallyavailable cryo-condenser suitable for providing a cryo-coolant jet inaccordance with an embodiment of the present disclosure.

FIGS. 13A-13I are schematic illustrations of representative types ofmicrowave pulse sequences that can be provided in accordance withparticular embodiments of the present disclosure.

DETAILED DESCRIPTION

In the present disclosure, depiction of a given element or considerationor use of a particular element number in a particular FIG. or areference thereto in corresponding descriptive material can encompassthe same, an equivalent, or an analogous element or element numberidentified in another FIG. or descriptive material associated therewith.The use of “/” in a FIG. or associated text is understood to mean“and/or” unless otherwise indicated. Additionally, unless explicitlystated otherwise, in the description herein, the recitation ofparticular numerical values or value ranges is taken to be a recitationof particular approximate numerical values or approximate value ranges.

As used herein, the term “set” corresponds to or is defined as anon-empty finite organization of elements that mathematically exhibits acardinality of at least 1 (i.e., a set as defined herein can correspondto a singlet or single element set, or a multiple element set), inaccordance with known mathematical definitions (for instance, in amanner corresponding to that described in An Introduction toMathematical Reasoning: Numbers, Sets, and Functions, “Chapter 11:Properties of Finite Sets” (e.g., as indicated on p. 140), by Peter J.Eccles, Cambridge University Press (1998)). In general, an element of aset can include or be a system, an apparatus, a device, a structure, astructural feature, an object, a process, a physical parameter, or avalue depending upon the type of set under consideration.

Embodiments of the present disclosure are directed to systems,apparatuses, devices, and processes configurable or configured forcontrollably and/or selectively applying electromagnetic energy, whichin various embodiments includes or is microwave energy, to a specimen,object, or sample (e.g., a biological sample) during a samplepreparation or fixation process. In various embodiments, a samplepreparation process includes or is a vitrification process involvingrapid or extremely rapid sample cooling, e.g., at an initial coolingrate on the order of approaching, at least substantially equal to, orgreater than 10,000 degrees Kelvin per second. During such avitrification process, microwave energy (e.g., pulsed microwave energy)can be directed or applied to a sample in particular manners to affector perturb water molecule dipole rotation energies in order to manage,reduce, disrupt, or substantially eliminate the formation of molecularH₂O aggregates (e.g., H₂O pentamer structures) associated with icecrystal formation. Consequently, ice crystal formation within the samplecan be at least substantially avoided or eliminated. Some embodiments inaccordance with the present disclosure are additionally or alternativelyconfigurable or configured for performing related or other types ofsample preparation or fixation processes (e.g., on a stand-alone basis,or on a selectable/combinable basis with respect to sample vitrificationprocesses such as those described herein), for instance, freezesubstitution processes.

Various embodiments in accordance with the present disclosure include atleast some of (a) a carrier or capsule structure, assembly, device, orelement, each of which is configured for carrying, housing, retaining,or holding a sample or specimen, and each of which includes at least onehigh or very high thermal conductivity surface, substrate, or supportmember configured for thermal communication or thermal energy transferwith a sample within the capsule; (b) an electromagnetic signalapplication apparatus, device, circuit, or structure configured forselectively delivering or applying electromagnetic energy or signals,such as microwave frequency signals, electromagnetic fields, orradiation, to or through portions of a capsule in which a sampleresides; and (c) a cooling system, apparatus, device, or unit configuredfor rapid or extremely rapid capsule cooling, such as by way of anapplication of at least one cryocoolant stream or jet to a capsule'shigh/very high thermal conductivity substrate. Various embodiments inaccordance with the present disclosure further include or are configuredfor use with an imaging system, such as an optical microscopy system,which can capture images of a sample before, during, and/or after asample preparation or fixation process.

Depending upon embodiment details, particular portions of a samplecarrier, an electromagnetic signal application apparatus, and/or acooling apparatus can be combined or integrated, for instance, in one ormore representative manners described below. Furthermore, in multipleembodiments, one or more portions of a sample carrier, anelectromagnetic signal application apparatus, and/or a cooling apparatuscan form a modular sample preparation or fixation apparatus or unit thatcan be combined or integrated with or adapted to a microscope configuredfor reflectance and/or transmission microscopy; a fluorescencemicroscope, such as a total internal reflection fluoroscopy (TIRF)microscope; a laser scanning confocal microscope; or another type ofmicroscope. In a representative implementation, a sample preparation orfixation apparatus in accordance with an embodiment of the presentdisclosure can be combined or integrated with or adapted to acommercially available microscope such as a Zeiss Axio Imager Variomicroscope.

Aspects of particular representative embodiments in accordance with thepresent disclosure are described in detail hereafter. Suchrepresentative embodiments are not intended to limit the scope of thepresent disclosure and/or any claims based thereupon. Unless definedotherwise, all technical and scientific terms used herein have the same,essentially the same, or an analogous meaning as technical andscientific terms commonly understood by one of ordinary skill in therelevant art.

Aspects of Representative System Embodiments

FIG. 3A is a schematic illustration of a sample preparation, fixation,processing, observation, and/or examination system 10 in accordance withan embodiment of the present disclosure. In an embodiment, a samplepreparation, fixation, processing, observation, and/or examinationsystem 10 includes a sample preparation or fixation apparatus 100 havinga capsule structure, assembly, device, or element (hereafter capsule orsample capsule) 110; a set of electromagnetic signal delivery elements130; at least one electromagnetic signal source 150; a thermal energytransfer apparatus 200; and a capsule environment management/controlunit 300. Various embodiments of the system 10 further include animaging system, apparatus, or device 50, such as a microscopy systemhaving a set of optical and/or imaging elements 55 such as one or moreobjective lenses and/or imaging devices (e.g., an image capture devicesuch as a CCD camera, which can be coupled to a computer system having adisplay device). The system 10 can also include a controller 80 (e.g., acomputer system, a microcontroller, or other type of programmable orprogrammed device), which can be configured for communicating with orcontrolling the electromagnetic signal source 150, the thermal energytransfer apparatus 200, the capsule environment control unit 300, andpossibly the imaging system 50.

The sample preparation or fixation apparatus 100 can include a set ofcoolant fluid sources 210 configured for fluid communication with thethermal energy transfer apparatus 200; and a set of intra-capsuleenvironment fluid sources 310 configured for fluid communication withinterior portions of the capsule 110. The capsule environment controlunit 300 can be configured to monitor, measure, manage, and/or controlparticular aspects of the capsule's internal and/or externalenvironment. For instance, the capsule environment control unit 300 canmonitor one or more capsule temperatures, for instance, by way of a setof temperature sensing elements or probes 302 such as a number ofthermocouples coupled to or carried by portions of the capsule 110(e.g., thermocouples distributed in a predetermined pattern relative toan interior or exterior portion, region, or surface of the capsule 110).The capsule environment control unit 300 can also facilitate, manage, orcontrol the flow of one or more substances and/or fluids (e.g., one ormore of a gas such as air, nitrogen, or argon; a liquid such as water ora growth medium; and a chemical substance intended to trigger areaction, response, or event within a sample) into/out of the capsule110 by way of a set of valves, openings, channels, conduits, and/orpassages 312.

FIG. 3B is a schematic illustration showing portions of a samplevitrification system in accordance with another embodiment of thepresent disclosure. In an embodiment, the system 10 includes a samplecapsule 110; first light optics 55 a (e.g., configurable or configuredfor focusing on or within a sample carried by the capsule 110); secondlight optics 55 b (e.g., configured for transmission microscopy); anintra-capsule fluid delivery and removal apparatus 302 (e.g., which cancorrespond to or form a portion of a capsule environmentmanagement/control unit 300 and an intra-capsule environment fluidsource 310 shown in FIG. 3A); a microwave applicator 132 (e.g., whichcan correspond to or form a set of electromagnetic signal deliveryelements 130 shown in FIG. 3A); a microwave generator 152 (e.g., whichcan correspond to or form a portion of an electromagnetic signal source150 shown in FIG. 3A); a cooling unit 200 configured for directing oneor more cryogenic coolant jets to the capsule 110; a correspondingcryocoolant supply reservoir 202, a cryocoolant return reservoir 204,and a cryogenic fluid source 210; an enclosure module or housing 102 inwhich various portions of the system 10 reside, for instance, as aself-contained or sealable/sealed subsystem module; and controlelectronics 82, which can be coupled to or form a portion of a controlsystem 80 shown in FIG. 3A.

In some embodiments, a sample processing, preparation, or fixationsystem 10 includes multiple sample capsules 110. For instance, a system10 can include a first through nth capsule 110 configured in apredetermined spatial arrangement (e.g., a rectangular array, or acircular/rotary configuration). Depending upon embodiment details, sucha system 10 can include one or multiple cooling units 200. For instance,a set of cooling units 200 can be configured to direct or applycryocooled fluid(s) to multiple capsules 110, e.g., to facilitate orenable sequenced or simultaneous sample vitrification processesinvolving multiple capsules 110. Furthermore, one or more cooling units200 can be configured for selectable or programmable displacementrelative to the capsules 110 (e.g., capsules 110 can be configured forrotary or turret-style displacement relative to one or more coolingunits 200), such that cryocooled fluid(s) can be directed or applied toparticular capsules 110 at particular times and/or in accordance with adesired or intended (e.g., programmably specified) sample vitrificationsequence. In embodiments that include multiple capsules 110, individualcapsules 110 can be sufficiently separated and/or thermally isolated(e.g., by way of insulative materials or the establishment of a partialvacuum between individual capsules 110) in a manner that ensures thatdistinct vitrification processes performed upon different capsules 110can remain thermally or substantially thermally independent (e.g., suchthat a first vitrification process directed to a first sample carried bya first capsule 110 does not affect or significantly affect a secondsample carried by a second capsule 110 or a second vitrification processdirected to the second sample).

In any of the foregoing embodiments, one or more capsules 110 can becarried by, coupled to, or form a portion of a positioning apparatus orstage assembly, such as a manual, semi-automated, or automated stageconfigured for 2-axis or 3-axis positioning or displacement (e.g., x, y,z, and/or θ positioning), in a manner understood by one of ordinaryskill in the relevant art.

Aspects of Representative Capsule Design, Sample Cryofixation, andMicrowave Energy Application

FIGS. 4A-4D are representative illustrations showing portions of samplechambers, receptacles, or capsules 110 in accordance with particularembodiments of the present disclosure. In general, a capsule 110includes a first or lower surface or layer; a second or upper surface orlayer 114; and an internal compartment 116 disposed between the firstand second layers 112, 114. In the description hereafter, the first orlower layer 112 is referred to as a substrate or substrate layer; andthe second or upper layer 114 is referred to as a cover.

The substrate 112 exhibits a high, very high, or extremely high thermalconductivity, and serves as a thermal energy transfer interface ormedium between a sample carried within the chamber's internalcompartment 116 and one or more cryogenically cooled substances ormaterials provided by a cooling unit 200. Depending upon embodimentdetails and/or the nature of a sample under consideration, one or moreportions of the sample can be in direct contact with the substrate 112,and/or one or more portions of the sample can be carried or suspended ina liquid medium such as water within the compartment 116.

The substrate 112 is additionally at least substantially transmissive ortransparent with respect to microwave and/or other electromagneticenergy wavelengths that can be directed into the capsule 110.Furthermore, in embodiments configured for transmission microscopy, thesubstrate 112 is at least substantially transmissive or transparent withrespect to one or more imaging wavelength ranges under consideration. Inmultiple embodiments, the substrate 112 includes or is a layer ofdiamond or sapphire. In a representative implementation, the substrate112 is a diamond disk having a diameter of approximately 8 mm.

The cover 114 forms one or more portions of an imaging interface orimaging interface layer that is at least substantially transparent ortransmissive with respect to a set of imaging wavelength ranges underconsideration, such as one or more of visible light wavelengths,infrared light wavelengths, and ultraviolet light wavelengths. Invarious embodiments, the cover 114 is transparent to optical microscopyillumination wavelengths, and includes or is a material such as glass,quartz, or plastic. In certain embodiments, the cover 114 can include orbe a material that is significantly or substantially thermallyinsulating (e.g., a plastic or polymer based material), which canenhance a rate at which the substrate 112, and hence a sample within thecompartment 116, can be cooled.

The compartment 116 forms a receptacle within which (a) at least onesample can be disposed; and (b) microwave and/or other electromagneticenergy or fields can be directed, applied, or delivered to thesample(s). The compartment 116 provides or establishes a gap, depth, orthickness between the substrate 112 and the cover 114, such that thesample can reside within the spatial (e.g., vertical) extent of the gap.Depending upon embodiment details and/or the nature of a sample underconsideration, the gap can have a depth or thickness on the order of onemicron, several microns, tens of microns, or hundreds of microns. Insome embodiments, the capsule 110 is configured to provide an adjustableor selectable gap, depth, or thickness, while in other embodimentsparticular capsules 110 (e.g., which can be removably transferred orselectably inserted onto/into the apparatus 100) exhibit a predeterminedgap, depth, or thickness.

Various embodiments in accordance with the present disclosure areconfigured for exposing a sample within the compartment 116 to microwaveenergy, signals, or radiation (e.g., which can be generated inaccordance with particular, predetermined, selectable, or programmablemicrowave signal parameters). A wide variety of electromagnetic signaldelivery element configurations, e.g., for directing microwave energyinto portions of the capsule 110, can exist, as further detailed below.In general, particular portions of the system 10 such as the capsule 110and/or a set of optical elements 55 can include one or more shieldinginterfaces or coatings to ensure or maximize the likelihood thatmicrowave and/or other electromagnetic energy directed into thecapsule's compartment 116 remains confined within an intended,predetermined, or limited spatial region.

For instance, as indicated in FIGS. 4A-4D, the capsule 110 can include afirst shielding layer 118 a carried by the capsule cover 114, and/or asecond shielding layer 118 b carried by the capsule substrate 112. Inembodiments in which the capsule's cover 114 carries or includes ashielding layer 118 a, the shielding layer 118 a is at leastsubstantially transparent to a set of imaging wavelength ranges underconsideration, and at least substantially non-distorting with respect toimaging requirements. In embodiments in which the substrate 112 carriesa shielding layer 118 b and the system 10 is configured for transmissionimaging, the shielding layer 118 b is at least somewhat or substantiallytransmissive or transparent to imaging wavelength ranges underconsideration. For instance, a shielding layer 118 a,b can include alayer based upon or formed from an Indium Tin Oxide (ITO), graphene,and/or other material (e.g., a metamaterial), which is transparent tooptical illumination wavelengths and optically non-distorting, and whichis electrically conductive and hence is suitable as a microwave fieldbarrier or shield. Additionally, a substrate-side shielding layer 118 bcan be structured or engineered in a manner that avoids substantiallyimpacting the substrate's thermal conductivity (e.g., a substrate-sideshielding layer 118 b should exhibit a high, very high, or extremelyhigh thermal conductivity, and/or minimally impact the substrate'stransfer of thermal energy from the sample to a cryogenically cooledsubstance or material provided by the cooling unit 200, such as by wayof a thin or very thin ITO-based shielding layer 118 b).

Depending upon embodiment details, a shielding layer 118 a-b can beessentially or entirely continuous across one or more portions of aplanar surface of a substrate 112 or a cover 114, or a shielding layer118 a-b can be patterned. For instance, in an embodiment, a substrate112 can carry a shielding layer 118 b (e.g., a thin layer or coating ofITO, gold, or graphene) that is patterned in a manner that providesapertures having dimensions that are sub-wavelength with respect toparticular wavelengths of microwave energy under consideration. In suchan embodiment, microwave energy originating from a source, device, orcircuit element external to the capsule 110 and incident upon thecapsule 110 at the substrate-side will be prevented from establishing apropagating mode within the capsule 110. However, an evanescentmicrowave field will couple into or enter the capsule 110 by way of theapertures. This evanescent microwave field can extend to or within oneor more portions of a sample and/or surrounding fluid, and hence canaffect or control sample vitrification by way of disrupting H₂O pentamerformation during a vitrification process that involves exposing thesubstrate 112 to a cryogenically cooled substance or material, asfurther detailed below.

In embodiments in which one or more optical elements 55 such as amicroscope objective lens are exposable or exposed to microwave fields,such optical elements 55 can be associated with or include shieldinglayers or structures. For instance, an objective lens backplane can beassociated with or include a conductive plate structure having anappropriate type of microwave field shielding layer or coating (e.g., anITO, graphene, and/or other material layer).

A number of temperature sensitive or sensing elements or devices can beconfigured for sensing, monitoring, or measuring temperatures ortemperature changes corresponding to the substrate 112 and/or otherportions of the chamber 110. In some embodiments a substrate 112 cancarry, include, or be coupled to a set of thermocouple orthermoresistive elements, which can be disposed in accordance with adesired or predetermined pattern such as an array. Certain embodimentscan include optical devices (e.g., infrared light detectors) configuredfor sensing or measuring temperatures or temperature changes.

Thermal coupling, energy transfer, or contact between the capsule'ssubstrate 112 and one or more cryogenically cooled substances and/ormaterials provided by a cooling unit 200 can be provided or establishedin multiple manners. In various embodiments, the cooling unit 200 isconfigured for directing at least one stream of cryogenically cooledliquid such as liquid nitrogen, liquid ethane, liquid propane, oranother cryogenic liquid to an outer or exterior surface of thesubstrate 112 which is exposable or exposed to the stream(s) in order tofacilitate or enable extremely rapid thermal energy transfer between asample within the capsule 110 and the cryogenically cooled liquid(s). Asindicated in FIGS. 5A and 5B, the cooling unit 200 can direct (e.g., byway of a set of cryocoolant applicator elements, conduits, or nozzles)at least one cryogenic coolant jet 220 a,b to the substrate 112 in oneor more manners, e.g., in a direction normal or substantially normal toa substrate plane that is parallel to or which forms an exterior planarsurface of the capsule 110, and/or at a given non-normal angle θ withrespect to such a substrate plane.

Various embodiments in accordance with the present disclosure can director apply cryogenically cooled liquid(s) to the substrate-side of thecapsule 110 in a manner that reduces or minimizes the effect(s) of astagnation point that can be associated with an inner or central region(e.g., centroid) of a cryocoolant stream or jet. A stagnation pointarises as a result of a low or very low local cryocoolant fluid velocityat a substrate impact interface at which cryocoolant velocity approachesor effectively equals zero. Consequently, a stagnation point can giverise to nonuniform substrate cooling. In some embodiments, a cryocoolantjet 220 b can be directed toward the substrate 112 at one or morenon-normal angles, e.g., an angle of θ degrees, or rapidly cycled,displaced, or swept within an angular range, in order to reduce orminimize stagnation points, where an angle θ or an angular range can bedefined with respect to a normal direction or axis relative to thesubstrate plane. Additionally or alternatively, multiple time sequencedor time multiplexed and/or pressure sequenced or pressure multiplexedcryocoolant jets 220 a,b can be directed toward the substrate 112 (e.g.,by way of multiple cryocoolant jet nozzles) to reduce or minimizestagnation points.

In some embodiments, the substrate 112 can include one or more shaped,contoured, or patterned portions or regions that can facilitate oreffectuate an enhanced thermal energy transfer efficacy or rate; reducedthermal stagnation effects; and/or the establishment or maintenance ofintended cryocoolant flow patterns (e.g., in view of thermal energytransfer efficacy associated with turbulent and/or laminar flow, forinstance, microstructures intended to facilitate disruption of laminarflow). For instance, FIGS. 6A-6H are schematic illustrations of acryocoolant jet 220 that is incident upon substrates 112 having one ormore patterned substrate regions. A substrate 112 can include or befabricated to carry or include micro-scale structural features such aschannels, grooves, and/or pillars that result in portions of thesubstrate 112 having reduced thickness. Such micro-scale structuralfeatures can be spatially or geometrically organized or distributed in auniform or non-uniform manner that facilitates or enables enhancedefficacy thermal energy transfer while substantially maintaining orretaining adequate substrate structural integrity. A cryogenic coolantjet 220 can be incident upon an external, exterior, or outer surface ofthe substrate 112 along a direction or at an angle α defined relative toparticular structural features. Depending upon embodiment details, adirection or angle of incidence corresponding to a given cryocoolant jet220 can be aligned or substantially aligned relative to particularstructural features such as channels, or at least partially misalignedrelative to particular structural features such as pillars. Dependingupon embodiment details, micro-structural features can have a verticalextent or depth of less than one to one, several, tens, or several tensof microns, and a lateral separation or periodicity of less than one toone, several, tens, or several tens of microns.

In various embodiments, the cooling system 200 provides aself-contained, closable, sealable, closed, or sealed system orsubsystem in which one or more cryocoolant liquids can be directed orapplied to the substrate 112 and internally recirculated, reused, orreapplied to the substrate 112. Such embodiments can include acryocoolant supply reservoir 202 and a cryocoolant return reservoir 204as indicated in FIG. 5B, which are coupled to at least one pressurized(e.g., high pressure) cryogenic fluid stream, jet, and/or spray deliveryapparatus, device, applicator, or nozzle. A cooling system 200 inaccordance with an embodiment of the present disclosure can include oneor more devices, components, or elements described in U.S. Pat. Nos.4,336,691; 5,044,165; and/or 7,637,187.

In general, a sample should be maintained at a desired, target, orpredetermined initial or reference temperature or within a desired,target, or predetermined initial or reference temperature range prior tothe application of a cryocooled substance or material to the substrate112. Sample pre-cooling, that is, cooling of the sample(s) away from orbelow a target initial or reference temperature or temperature rangeprior to a time at which thermal energy transfer of contact between acryocooled substance or material with the substrate 112 is intended tooccur, can augment nucleation sites and corresponding ice crystalgrowth. Hence, sample pre-cooling should generally be avoided.Furthermore, the application of a cryocooled substance or material tothe substrate 112 should occur in a manner that transitions thesubstrate 112, and hence the sample carried by the capsule's chamber116, from the initial or reference sample temperature or temperaturerange to a sample vitrification temperature as rapidly as possible.

In order to minimize the likelihood or extent of sample pre-cooling, orat least substantially avoid sample pre-cooling, a system 10 orapparatus 100 in accordance with particular embodiments of the presentdisclosure can include one or more types of chamber or sampletemperature establishment, regulation, or maintenance mechanisms orelements. For instance, the substrate 112 and/or the cover 114 caninclude conductive portions or elements (e.g., conductive lines orwires, or a conductive shielding layer 118 a,b itself) that can becoupled to an electrical current source, and which can provide ordeliver a controllable or monitorable amount of thermal energy (e.g.,small amounts of heat, such as by way of ohmic or resistive heating) toportions of the capsule 110. The system 10 or apparatus 100 canadditionally or alternatively include a number of optical heatingelements configured for applying or delivering thermal energy toportions of the capsule 110, such as infrared LEDs or optical fibers.Moreover, portions of a system 10 or apparatus 100 configured forcarrying microwave signals can deliver or apply microwave energy to thesample(s) and/or the capsule's compartment 116 at a wavelength,wavelength range, and/or intensity that results in sample and/orcompartment 116 temperature establishment, maintenance, orselectable/selective heating. Some embodiments can additionallyestablish, provide, or inject a neutral gas (e.g., a dry gas) thatfacilitates thermal insulation, e.g., a heavier dry gas such as Argon,into a spatial region of the cooling unit 200 between a cryojet nozzleterminus or tip and the capsule 110.

In some embodiments, the cooling unit 200 includes at least onebreakable or pierceable membrane (e.g., a polymer membrane) disposedbetween the cryocoolant jet(s) and an external, exterior, or outersubstrate surface. More particularly, each such membrane can serve as athermal energy transfer regulation or barrier element between thecryocoolant jet(s) and the substrate 112. The membrane(s) can be brokenor pierced in response to an incident cryocoolant jet pressure or forcethat exceeds a predetermined or target level or value (e.g., one or moregrams per square centimeter), which can occur at an intendedvitrification initiation time or in response to a trigger event.Furthermore, the cooling unit 200 can be configured to establish ormaintain a partial vacuum within a spatial region between a breakablemembrane and the capsule 110, which provides or enhances a thermalbarrier between a cryojet nozzle tip and the sample(s). In otherembodiments, the cooling unit 200 can include an ultra fast mechanicalshutter mechanism configured to selectively isolate a set of cryocoolantjets from the substrate 112 before an intended vitrification initiationtime or the occurrence of a trigger event.

A likelihood or extent of sample pre-cooling can also be reduced orminimized by way of a cryocoolant jet displacement mechanism (e.g., asolenoid based or magnetic displacement mechanism) that is configuredfor keeping the cryocoolant jet(s) at a minimum intended distance awayfrom the substrate 112 prior to an intended vitrification initiationtime or the occurrence of a trigger event, and further configured forrapid displacement (e.g., relative or parallel to or along a directionor axis normal to a planar substrate 112) to a position proximate oradjacent to the substrate 112.

As indicated above, depending upon embodiment details, microwave energycan be directed, delivered, or applied to portions of the capsule 110and/or one or more samples therein in a variety of manners. In someembodiments, a set of electrically conductive elements or linesconfigured for carrying microwave signals can be disposable or disposedwithin the cooling unit 200, below and substantially normal to thesubstrate 112, such that the set of electrically conductive elements areconfigured for providing, delivering or applying microwave energy toparticular portions of the capsule 110. In some embodiments, such amicrowave field application device can correspond to or be analogous toa microwave drill, in a manner understood by one of ordinary skill inthe relevant art. FIG. 7A is a schematic illustration of a microwaveprobe 122 in accordance with an embodiment of the present disclosure,which includes a center conductor and a set of outer conductors. Atleast one microwave probe 122 can be positionable or positioned suchthat microwave energy is deliverable or delivered to one or more targetregions within the capsule 110 as a result of a microwave field or fielddistribution provided by the center and outer conductors. A verticaloffset between the center conductor and the outer conductor(s) and/or ahorizontal or lateral offset between the center conductor and the outerconductor(s) can be selected relative to microwave wavelengths underconsideration, such that a terminal portion or end of the microwaveprobe 122 can provide or couple near-field or evanescent wave energy toportions of the cavity 110 (e.g., by way of sub-wavelength geometry or anear-field microwave conductor separation, gap, aperture, opening, orhole corresponding to a terminal portion or end of the microwave probe122). For instance, in some embodiments, the microwave probe 122 a isconfigured to provide near-field or evanescent wave coupling ofmicrowave energy into a sample that is carried at or within an expectedportion of the compartment 116. Thus, during a sample vitrificationprocess, the center conductor can be positioned at a normal or verticalgap or distance relative to the underside or exterior surface of thesubstrate 112 such that evanescent wave coupling with the compartment116 and/or sample can occur. As indicated in FIG. 7A, a cryogeniccoolant jet 220 can be directed toward or to the substrate 112 at anon-normal angle of incidence θ, such that cryocooled liquid flowswithin the gap between the center conductor and the substrate 112.

In some embodiments, a microwave energy application or delivery devicecan be coupled to or associated, combined, or integrated with portionsof a cryocoolant jet apparatus to form a microwave field—cryocoolantapplicator that can (a) generate microwave fields suitable fordisrupting H₂O pentamer formation during a vitrification process; aswell as (b) carry or output one or more cryocooled liquid streams orjets.

For instance, FIG. 7B is a schematic illustration of a microwaveprobe/cryocoolant applicator 122 b in accordance with an embodiment ofthe present disclosure, which is configured for providing, supplying, orestablishing a cryocoolant jet by way of cryocoolant liquid flow betweena center conductor and an outer conductor, such that the cryocoolantliquid can be output, ejected, or shot from a terminal portion or end ofthe field microwave probe/cryocoolant applicator 122 b and directedtoward or to the substrate 112 (e.g., in a direction normal orsubstantially normal to a plane of the substrate 112). The terminalportion or end of the microwave probe/cryocoolant applicator 122 b canthus form a nozzle structure for delivering cryocooled liquid to thesubstrate 112. FIG. 7C is a schematic illustration of a microwaveprobe/cryocoolant applicator 122 c in accordance with another embodimentof the present disclosure, which is configured to provide, supply, orestablish a cryocoolant jet by way of cryocoolant liquid flow within achannel or passage defined by a center conductor. In other embodiments,aspects of FIGS. 7B and 7C can be combined. In some embodiments, amicrowave probe or a microwave probe/cryocoolant applicator 122 can beconfigured to carry, propagate, or transmit light within a gap between acenter and an outer conductor, or within a center conductor passage, tofacilitate transmission microscopy.

Microwave fields can also be delivered to a sample within a capsule 110in additional or other manners. For instance, some embodiments inaccordance with the present disclosure generate or deliver microwavefields by way of stripline or co-planar waveguide elements, which enablemicrowave energy transport along patterned conductors such thatmicrowave fields can be controlled to initiate and terminate relative toparticular portions of conductive lines or branches. Embodiments thatinclude stripline or co-planar waveguide elements can be compact orhighly compact, and can facilitate tight microwave field confinementand/or minimal microwave field leakage.

FIGS. 8A-8D are schematic illustrations of a microstrip capsulestructure or assembly 110 in accordance with an embodiment of thepresent disclosure. In an embodiment, the microstrip capsule assembly110 includes a dielectric support member or substrate 120 that includesat least one sample or specimen compartment 116, and which carries orincludes a set of microwave signal elements coupled to a microwavesignal source or generator 152 (e.g., a microwave amplifier). The set ofmicrowave signal elements is configured for providing, delivering,applying, or coupling microwave fields to internal portions of thecompartment(s) 116, as further detailed below.

Depending upon embodiment details, the substrate 120 can be fabricatedas one or more layers using one or more materials. In some embodiments,the substrate 120 can include or be portions of a printed circuit board(e.g., provided by Rogers Corporation Advanced Circuit Materials (RogersCorporation, Connecticut, USA, www.rogerscorp.com). One or more portionsof the substrate 120 can additionally or alternatively be coupled to,carry, include, or be a high, very high, or extremely high thermalconductivity material, such as diamond or sapphire.

The set of microwave signal elements includes a number of microwavetransmission lines 122 and a ground signal path, element, or plate 124.In several embodiments, the set of microwave signal elements furtherincludes a number of impedance matching or tuning structures or elements126, such as a set of integrated stub tuner elements (e.g., multistubtuners), such that the set of microwave signal elements can be coupledto and impedance matched with a set of conventional or standardimpedance (e.g., 50 Ohm) signal lines. The matching structures orelements 126 can include non-adjustable and/or adjustable (e.g.,microelectromechanical (MEMS) based and/or microfluidic liquid based)impedance matching elements.

In general, the set of microwave signal elements includes at least onemicrowave transmission line 122 configured for carrying microwavefrequency electrical signals to, across, over, under, into, and/orthrough portions of the compartment(s) 116. The microwave transmissionline(s) 122 can exhibit various spatial or geometric configurations,such as a straight or substantially straight stripline pattern, or ameander pattern. The microwave transmission lines 122 and the groundplate 124 can be fabricated using one or more conductive or highlyconductive materials (e.g., copper or gold). An individual of ordinaryskill in the relevant art will understand that the set of microwavesignal elements can be directly or substantially directly fabricated orintegrated upon and/or within portions of the substrate 120, forinstance, by way of microfabrication techniques (e.g., corresponding tosemiconductor device or integrated circuit fabrication processes).

The compartment 116 is configured for carrying, retaining, orsurrounding a sample (e.g., a liquid within which a biological specimenis disposed), and can be fabricated or integrated upon or withinportions of the substrate 120. For instance, the compartment 116 can bea machined, micromachined, milled, etched, and/or molded opening orrecess within the substrate 120. Additionally or alternatively, thecompartment 116 can be an insertable structure (e.g., an insertconfigured for carrying or at least partially retaining a liquid, and abiological specimen disposed therein). In some embodiments, a microstripcapsule assembly 110 includes a number of microfluidic channels 117configured for fluid communication (e.g., gas and/or liquid flow) withthe compartment 116, which can be fabricated or integrated upon orwithin the substrate 120 in a manner identical, substantially identical,or analogous to that for the compartment 116 as understood by one ofordinary skill in the relevant art. Such embodiments can include or becoupled to additional or other microfluidic structures or elements(e.g., fluid flow control elements), in a manner also understood by oneof ordinary skill in the relevant art.

The microstrip capsule assembly 110 can further include a coverstructure, member, or element 114 configured for overlaying or coveringthe compartment 116. The cover 114 can be substantially transmissive ortransparent with respect to one or more imaging wavelength ranges underconsideration (e.g., optical imaging wavelengths) in order to facilitateor enable imaging, focusing, or image capture therethrough. The cover114 can additionally carry or include one or more electricallyconductive materials (e.g., a layer of ITO) and/or structures (e.g.,transmission line or electrode elements) configured for providingelectrical continuity between or across distinct or separate portions ofa given microwave transmission line 122. Electrically conductivematerials carried by the cover 114 can be substantially transmissive ortransparent relative to imaging wavelength ranges under consideration,or electrically conductive materials can be patterned or routed in amanner that minimizes or avoids obstructing or adversely affectingimaging, focusing, or image capture (e.g., which substantially orentirely avoids obstructing and/or distorting optical signalspropagating along an optical/imaging axis corresponding to an opticalmicroscopy system). Depending upon embodiment details, electricalcontinuity between a microwave transmission line 122 and electricallyconductive portions of the cover 114 can be provided by way of direct orsubstantially direct electrical coupling or contact, or by way of a gapfeed, in a manner understood by one of ordinary skill in the relevantart.

In addition or as an alternative to the foregoing, in certainembodiments, a cooling unit 200 can include a selectively displaceable(e.g., vertically displaceable) cryogenically cooled plate, stage, ordisc configured for establishing contact with the substrate 112. Forinstance, the cooling unit 200 can include a cryogenically cooled platethat can be pre-cooled to an intended or desired cryogenic temperature(e.g., by way of exposure to or at least partial immersion in liquidnitrogen or another cryofluid), and which can be controllably andrapidly displaced to establish contact with an exterior or outer surfaceof the substrate 112 to initiate sample vitrification. The cryocooledplate and the substrate 112 can include very smooth/uniformly planarsurfaces (e.g., machined/polished parallel surfaces) configured forestablishing intimate contact with each other. The cryocooled plate caninclude or be carried by a positional accommodation mechanism, such as aset of springs or an elastomeric material, to facilitate auto-adaptivepositional adjustment (e.g., angular tilt adjustment) in the event thatsurfaces intended for maximum intimate planar contact exhibit a certaindegree of non-planarity. Additionally or alternatively, the cryocooledplate can carry or include one or more material layers or coatings(e.g., an ITO layer) on an exterior surface intended for contact withthe substrate 112 that can facilitate enhanced intimacy contact with thesubstrate 112 and/or enhanced efficacy thermal energy transfer.

A cooling unit 200 can include a port configured for automatically orsemi-automatically loading (e.g., on a user-selectable basis) new orunused cryocooled plates into the cooling unit 200 or unloading used orinsufficiently planar cryocooled plates from the cooling unit 200.Furthermore, a cooling unit 200 can be configured for internallycarrying multiple cryocooled plates therein, such that a new or unusedcryocooled plate can be selected and/or loaded into an appropriatespatial position relative to the substrate 112 prior to a samplevitrification process, and a cryocooled plate that has been used morethan a selectable or predetermined number of times or which exhibitsinsufficient planarity or surface defects can be automatically orsemi-automatically displaced or offloaded to a different spatialposition following a sample vitrification process. In certainembodiments, a cryocooled plate and the substrate 112 can carry one ormore alignment members (e.g., at outer portions) configured for matingengagement with each other.

In an embodiment involving a cryocooled plate, a microwave signal sourcecan be coupled to the cryocooled plate such that microwave signals canbe carried by or applied to the cryocooled plate itself. Hence, thecryocooled plate can serve as a microwave excitation source configuredfor exposing the sample(s) within the chamber 110 to microwave fields inorder to disrupt or prevent H₂O pentamer formation during avitrification process.

In various embodiments, a microwave signal source or generator 152 caninclude or be a microwave amplifier such as a solid state microwaveamplifier configurable or configured for outputting microwave signalshaving a frequency of between approximately 2 GHz-18 GHz (e.g., about2.4-2.45 Ghz, 5.8 GHz, or 10 GHz or higher). Some embodiments include orutilize WiFi or analgous types of signal generators or componentsconfigured to provide up to, for instance, 10 W of power. Certainembodiments can include or utilize a Voltage Controlled Oscillator (VCO)configured for outputting a signal that is modulated by a PIN switch,where the modulated signal can be further amplified. Other embodimentscan include or use a magnetron (e.g., a pulsed magnetron).

Microwave energy, signals, fields can be provided, delivered, applied,and/or coupled (e.g., by way of near field or evanescent wave coupling)to portions of a chamber in various manners, such as by way of amicrowave probe or applicator; a set of patterned or integratedmicro-scale transmission lines; resonant coupling; and/or a travelingwave apparatus or device. In general, microwave energy is providable orprovided to a sample at a power density that is sufficient to affect,modulate, or prevent ice crystal formation or nucleation processes, butwhich avoids adversely affecting the sample or the sample vitrificationprocess. In various embodiments, microwave energy, signals, or fields isprovided in one or more pulsed manners to facilitate or effectuate ahigh or very high instantaneous microwave pulse power density that candisrupt or prevent H₂O pentamer formation, yet which itself avoids orsubstantially avoids sample heating. More particularly, in multipleembodiments, microwave pulses are provided in a manner such that pulsesor pulse sequences are timed or synchronized relative to ice crystalgrowth dynamics in a manner that corresponds to expected, simulated, ormeasured ice crystal nucleation/formation processes, for instance, icecrystal nucleation that occurs within a nucleation time or interval ofapproximately 300 microseconds (e.g., in which case microwave pulses areapplied at time intervals less than or equal to approximately 300microseconds), and substantially complete solidification withinapproximately 30 microseconds.

FIGS. 8E-8G are schematic illustrations of a coplanar microstrip capsulestructure or assembly 110 in accordance with an embodiment of thepresent disclosure. In an embodiment, the coplanar microstrip capsulestructure 110 includes a set of coplanar microwave signal transmissionlines 122 a 1, 122 a 2, 122 b 1, 122 b 2 which are carried by or betweena first and a second dielectric substrate or laminate structure 120 a,b,and which are disposed between a first ground plane structure 126 a anda second ground plane structure 126 b, as indicated in FIGS. 8F and 8G.A specimen or sample compartment or chamber 116 can be disposable ordisposed between transmission line segments as shown, in a manneranalogous to that described above. In several embodiments, thetransmission lines 122 a,b can reside within a bondable or bondedinterface 121 that structurally couples or assembles the first andsecond ground plane structures 126 a,b. Depending upon embodimentdetails, the bondable interface 127 and the transmission lines 122 a,bcan be formed independent of or separate from one or both of the groundplane structures 126 a,b, after which appropriate bonding between thebondable interface 127 and one or both ground plane structures 126 a,bcan occur. The manner in which the set of transmission lines 122 a, 122b is disposed between the ground plane structures 126 a,b provides tightelectromagnetic field confinement, and facilitates effective shielding.

While the set of transmission lines 122 a,b shown in FIGS. 8E-8Gcorresponds to a pair of conductive traces, other embodiments can bescaled to include a larger number of conductive traces, depending uponembodiment details, electrode configuration, intended microwaveradiation distribution characteristics, and shielding considerations.Furthermore, other/additional conductive traces can be added on outeredges of the structure 110, or between trace pairs to provide signalisolation and/or shielding between transmission lines 122 and/or thestructure's edges. Additionally or alternatively, various types ofcircuit structures (e.g., vias, slots, and/or stubs) can be integratedinto portions of the structure 110. Moreover, one or more types ofcutouts or recesses on feed ends can be provided to make space forand/or facilitate microwave signal delivery into internal portions ofthe compartment 116. Coupling to a set of electrodes or electrodestructures that facilitate microwave signal delivery to internalportions of the compartment 116 can be achieved by way of an appropriateelectrical structure, a recess, or a gap feed, depending upon embodimentdetails. Some embodiments include a signal balancing device such as abalun, which can be externally coupled to or integrated as part of thestructure 110. Microfluidic channels can also be provided in a manneranalogous or generally analogous to that described elsewhere herein.

In view of the foregoing, FIG. 8H is a schematic illustration of ageneralized microstrip capsule structure or assembly 110 in accordancewith an embodiment of the present disclosure. In an embodiment, thegeneralized structure 110 includes at least one dielectric substrate orlaminate 120 that carries a set of microwave transmission lines 122; aset of microwave functional elements 123, a set of microwave couplingelements 125, possibly a set of microfluidic elements 127; and anelectrode based microwave signal applicator 129 (e.g., comprising a setof electrodes) by which microwave energy can be delivered into portionsof a sample or specimen chamber or compartment 116. The set of microwavefunctional elements 123 can include one or more of matching devices(e.g., stubs, or quarter wave transformers); a balun to convert betweenbalanced and unbalanced signal transmission lines 122; a set of phaseshifters; a set of power dividers; a set of isolators; a set ofmicrowave opens, shorts, gaps, slots, plated or unplated vias; couplers,controlled length and controlled impedance transmission line elements;microwave resistors, capacitors, or inductors; or other microwavestructures or elements as understood by one of ordinary skill in therelevant art.

The set of coupling elements 125 is configured for communicating ordelivering microwave signals to the electrode applicator/set ofelectrodes 129, and can include one or more of metal contact elementsand associated mechanical pressure or force application devices thatestablish electrical signal communication between metal-to-metalcontacts; intermediate conductive film(s) between metal-to-metal contactelements, which can facilitate reduced or low contact resistance underpressure or bonding conditions; contact elements that can be selectivelyand rapidly released after freezing; and gap feeds or gap couplersdesigned to couple microwave energy from the transmission lines to theelectrode applicator 129.

In several embodiments, the size of one or more portions of a capsulestructure or assembly 110 is correlated with or corresponds to astandard microscope slide size, such that the capsule structure 110 andassociated elements of a sample preparation or fixation system 10 can bereadily carried by, used with, or removably/matingly engaged with one ormore conventional or generally conventional types of sample/specimenimaging devices, such as an optical microscope. Aspects of arepresentative embodiment of such a capsule structure 110 is describedin detail hereafter with respect to FIGS. 9A-11B.

FIGS. 9A-9D are schematic illustrations of portions a microstrip-basedcapsule structure or assembly 400 in accordance with yet anotherembodiment of the present disclosure. FIGS. 10A-10I are illustrations orimages corresponding to aspects of the microstrip-based capsulestructure 400 of FIGS. 9A-9D. In an embodiment shown in an exploded viewin FIG. 9A, the capsule structure 400 includes an extremely high thermalconductivity substrate (hereafter “thermal energy transfer substrate”)112, such as a diamond or sapphire plate or disk, having an underside orbottom face that forms a physical interface to which a cryo-coolant jet220 can be directed, and an upper side or top face that forms a bottomsurface of a specimen or sample compartment, chamber, or cell 116 withinwhich a biological sample or specimen can be disposed. As will beunderstood by one of ordinary skill in the relevant art, a biologicalsample can be grown or placed on the upper face of the thermal energytransfer substrate 112. The capsule structure 400 further includes aholding ring 410 that forms exterior portions of the compartment 116;and a microfluidic ring insert 420, which forms internal side walls ofthe compartment 116. More particularly, the holding ring 410 isconfigured for carrying, holding, or retaining the thermal energytransfer substrate 112, as well as the microfluidic ring insert 420,which can be matingly engaged with the holding ring 410. Themicrofluidic ring insert 420 forms an internal region of the compartment116 that forms a microfluidic cell, which is configured for carrying aspecimen and exposing the specimen to a fluid environment by way ofmicrofluidic elements. The microfluidic cell can include a set offlexible fluid capillaries 450 that can be coupled to or inserted intothe microfluidic ring insert 420, and which facilitate or effectuatefluid delivery into and fluid withdrawal from the microfluidic cell 416,or fluid circulation therein.

The capsule structure 400 further includes a microwave applicatorcoverslip 460, which forms a cover 114 for the compartment 116, andwhich carries a set of excitation elements 500, which can be patternedmicrowave signal conductors or traces (e.g., an underside of thecoverslip) that serve as electrodes by which microwave energy can beprovided to internal portions of the microfluidic ring insert 420 tothereby irradiate a sample disposed within the microfluidic cell 116.The microwave applicator coverslip 460 can be manufactured performingstandard conductive trace patterning techniques upon a support member ormaterial such as a standard microscope coverslip (e.g., a standard no.1.5 square quartz coverslip having a thickness of 0.17 mm, and a sidelength of 22 mm), such as by way of performing optical masking,photolithograpy, etching, and possibly electroplating to selectivelyform or define conductive traces in accordance with a predeterminedpattern defined by a mask (e.g., a photomask).

Taken together, the thermal energy transfer substrate 112, themicrofluidic holding ring 410, the ring insert 420, and the microwaveapplicator coverslip 460 form or provide a hermetically scalablemicrofluidic microwave delivery chamber module or sample cell 402, byway of which (a) a specimen or sample disposed within the microfluidicring insert can be exposed to one or more types of fluids (e.g., abuffer and/or nutrient solution to maintain cell viability; or achemical substance that can provide a chemical impulse to rapidly changethe chemical environment to which a sample is exposed; or a chemicalsubstance such as glutaraldehyde, which can be used in a microwaveassisted chemical fixation procedure in which cryofixation orultra-rapid freezing does not or need not occur); (b) the specimen orsample can be jet frozen as a result of exposure of the underside of thethermal energy transfer substrate 112 to a cryogenic cooling jet 220,and corresponding high efficiency ultra-rapid cooling of the sample frombelow or underneath the sample; and (c) which can be transferred to acryogenic environment such as a dewar containing LN, and/or a lowtemperature high resolution imaging system, for instance, a scanningelectron microscope (SEM), a scanning helium ion microscope (SHIM), orother type of very high resolution microscope (e.g., an atomic forcemicroscope (AFM)) having a cold stage configured for cryo-microscopy.

In several embodiments, the sample cell 402 exists in two joinable orsealable (e.g., hermetically sealable) portions, namely, a top or upperportion and a bottom or lower portion. The top portion includes themicrowave applicator coverslip 460, the microfluidic ring insert 420,the capillaries 450, and the holding ring 410, each of which can bejoined together (e.g., by way of appropriate bonding) to form a singleor integrated unit prior to combining with the bottom portion, whichincludes the thermal energy transfer substrate 112. An embodiment of anassembled microfluidic microwave delivery chamber module or sample cell402 is shown in perspective view in FIG. 9B. One or more portions of themicrowave delivery chamber module or sample cell 402, such as its topportion, can form a disposable unit that can be manufactured reliably aninexpensively.

In several embodiments, a sealing structure or apparatus, which caninclude a hemostat type mechanism, can securely apply pressure or forceto or across portions of the microwave delivery chamber module or samplecell 402 to facilitate hermetic sealing. The sealing structure orapparatus simultaneously aligns (e.g., self-aligns) and clamps thethermal energy transfer substrate 112, the holding ring 410, and themicrowave applicator coverslip 460. In some embodiments, a sealingapparatus can include a set of forceps configured for holding andsealing the microwave delivery chamber module or sample cell 402.

The holding ring 410 serves to securely retain the thermal energytransfer substrate 112 as well as the microfluidic ring insert 420 andthe sample (e.g., a vitrified biological specimen) from below. Theholding ring 420 can be formed or machined using one or more materialsthat (a) exhibit high or very high material stability and thermalstability at cryogenic temperatures; (b) exhibit microwavecompatibility; (c) can be machined or formed in accordance with tight orvery precise mechanical tolerances; and (d) is vacuum compatible orexhibits minimal or negligible outgassing under vacuum conditions. In arepresentative embodiment, the holding ring 410 includes or is made ofVespel, and/or another suitable type of polymer material. The holdingring 410 can carry a set of fiducial markers that can be identifiedunder an optical microscope as well as a SEM, a SHIM, or other type ofvery high resolution microscope, in order to facilitate correlativemicroscopy procedures. The thermal energy transfer substrate 112 canalso carry one or more types of fiducial markers or substrate locationreference structures in order to facilitate correlative microscopyprocedures. However, following sample vitrification, fiducial markerscarried by the thermal energy transfer substrate 112 may not bedetectable, imageable, or viewable. Thus, in various embodiments, themicrofluidic microwave delivery chamber module or sample cell 402 caninclude a first set of fiducial markers internal to the compartment 116and a second set of fiducial markers external to the compartment 116.

FIG. 9C is a plan view showing portions of a microfluidic ring insert420 in accordance with an embodiment of the present disclosure. In anembodiment, the microfluidic ring insert 420 includes a main body 422 inwhich a set of micro-channels 424 are formed; a set of jet ports 426capable of fluid communication with the micro-channels 424; and alaminar, substantially laminar, or approximately laminar flow region 430configured for fluid communication with the set of jet ports 426. Atleast one fluid input capillary 452 and at least one fluid outputcapillary 454 can be inserted into the main body 422 and fluidicallycoupled to corresponding micro-channels 424 therein, such that fluid canbe communicated or conveyed into and out of the laminar flow region 430.In some embodiments, the main body 422 is fabricated or machined toinclude tapered micro-channel portions that can provide a securefriction fit fluid seal (e.g., by way of Inner-Lok™ friction fitstructures or elements, Polymicro Tehnologies, Phoenix, Ariz. USA) tothe fluid input and fluid output capillaries 452, 454, in a mannerindicated in FIG. 9D. The capillaries 452, 454 can be made of glass, andcoated with a cryogenic compatible jacket to enable flexure withoutcracking. The capillaries 452, 454 can be fluidically coupled to otherfluid transfer structures (e.g., other capillaries or tubes) usingpush-fit connector elements that facilitate quick connect/disconnect.

The microfluidic ring insert 420 and the flexible fluid capillaries 452,454 are configured for providing a microfluidic cell, chamber, orcompartment having minimal dead volume and an engineered laminar flowregion 430 that is fed by the capillaries 454, 454. The jet ports 426can affect or control the flow of fluid into and across the laminar flowregion 430, and hence the flow of fluid toward, to, across, and/oraround a specimen or sample (e.g., a biological specimen) that resideswithin the laminar flow region 430. Particular representative manners inwhich the microfluidic ring insert 420 can be implemented, including thejet ports 425 are provided by Elisabeth Verpoorte and Nico F. De Rooijin “Microfluidics meets MEMS,” Proceedings of the IEEE, Vol. 91, No. 6,June 2003.

The microfluidic ring insert 420 can be made using a moldable material.For instance, the microfluidic ring insert 420 can be injection moldedusing a material such as polydimthylsiloxane (PDMS), which exhibitssuitable material and thermal properties in a manner analogous to thatindicated above for the holding ring 410, as well as compatibility withbiological specimens or samples. For injection molding, a stainlesssteel mold or form can provide a microfluidic ring insert 420 havingsmooth surfaces and minimal surface roughness. The holding ring 410, theflexible capillaries 450, and the microwave applicator coverslip 460 canbe placed in the mold such that the PDMS microfluidic ring insert 420spatially forms around them, and such parts are automatically bondedtogether. The open ends of the capillary tubes 452, 454 are temporarilysealed, prior to molding, in order to prevent backflow of liquid PDMStherein when injection molding occurs. Silanization can be carried outon mold parts to passivate surfaces and enable the formed microfluidicring insert 420 to easily disengage from the mold. Additionally, thesurfaces of the mold that come into contact with the microwaveapplicator coverslip 460 are maintained in a highly flat and evencondition to prevent the application of uneven stress on the coverslip460 or cracking the coverslip 460 when the mold is sealed shut.

In various embodiments, the holding ring 410 and possibly themicrofluidic ring insert 420 are configured for carrying at least onefracture initiation element 412, such as a tungsten wire or a wedge,which can facilitate or enable in-situ freeze fracturing (e.g., when themicrofluidic microwave delivery chamber module 402 is carried by a stageor platform assembly inside a very high resolution imaging device, suchas a SEM or SHIM. The fracture initiation element 412 can be carried byor secured or embedded within the holding ring 410 and possibly themicrofluidic ring insert 420 at a predetermined height or distance(e.g., approximately 10 microns, 25 microns, or 50 microns, dependingupon a specimen or sample under consideration) away from an exposedsurface (e.g., the upper surface) of the thermal energy transfersubstrate 112 that carries a frozen specimen or sample, to facilitatesample imaging at a predetermined freeze depth or height relative to theupper surface of the thermal energy transfer substrate 112. Arepresentative type of fracture initiation element 412 is shown in FIG.9E.

As indicated in FIGS. 10A and 10B are plan view and side viewillustrations of portions of a microstrip-based capsule assembly 400 inaccordance with an embodiment of the present disclosure. As indicated inFIGS. 10A and 10B, the assembly 400 further includes a dielectricsubstrate 600 such as a printed circuit board (PCB), on which conductivetraces 610 reside. The dielectric substrate 600 can be shaped anddimensioned to have a size that matches or substantially matches thesize of a standard microscope slide. In a representative implementation,the dielectric substrate 600 can include a Rogers RO3010 laminate (10GHz), or a Rogers RO4003C laminate (5.85 GHz). The dielectric constantsof Rogers RO3010 and RO4003C and are 10.2 and 3.55, respectively.

In several embodiments, the conductive traces 610 on the dielectricsubstrate 600 form a set of Wilkinson power dividers, which provideisolation and minimize crosstalk between output ports, with the additionof surface mount RF resistors 612 (e.g., 100 Ohm resistors) whilemaintaining a matched condition among input and output ports, in amanner understood by one of ordinary skill in the relevant art. TheWilkinson power dividers can include resistors 612, as also understoodby one of ordinary skill in the relevant art.

The conductive traces 610 can be coupled to a microwave signal source byway of a set of connectors 700, such as microwave subminiature version A(SMA) connectors. A holding base or stage/platform structure 800 cancarry or support the microstrip-based capsule assembly 400, such thatthe thermal energy transfer substrate 112 is above a cryogenic coolingjet 220, which can be supplied by a cryo-jet nozzle 222.

The microwave applicator coverslip's excitation elements 500 havedifferent dimensions than the dielectric substrate's conductive traces610 due to the dielectric properties of the quartz coverslip on top andthe aqueous medium below the excitation elements 500. Numericalsimulation can be utilized to determine excitation element width, suchthat a desired electromagnetic field distribution within the sampleregion 116 can be achieved. In a representative embodiment, anexcitation element width corresponding to a microwave frequency of 5.85GHz can be approximately 0.5 mm. A corresponding excitation elementthickness can be selected to achieve low resistivity and reliableelectrical contact with the dielectric substrate's conductive traces610.

FIGS. 10C-10E are images showing portions a representativeimplementation of the microstrip-based capsule assembly 400 of FIGS.9A-10B, positioned relative to a platform or stage of an opticalmicroscope. In an embodiment, electrical signal communication betweenthe microwave substrate's conductive traces 610 and the microwaveapplicator coverslip's excitation elements 500 can occur by way ofdirect metal-to-metal contact therebetween, which can be facilitated byway of mechanical pressure or force that results in reliable electricalcontact. As indicated in FIG. 10E, such mechanical pressure or force canbe provided by a clamp structure that is disposable over the microwaveapplicator coverslip 460, and which can apply as a gentle downwardpressure or force upon the microwave applicator coverslip 460 toestablish electrical contact between the coverslip's excitation elements500 and the microwave substrate's conductive traces 610.

Various configurations, layouts, or designs are possible for thecoverslip's excitation elements 500, for instance, depending upon amicrowave frequency under consideration. For instance, FIG. 10F includesimages depicting multiple representative types of excitation elementdesigns in accordance with particular embodiments of the presentdisclosure. In general, excitation elements 500 are designed to (a)minimize electrode coverage relative to the surface area of thecoverslip 460, which provides optical access for sample imaging; and (b)maximize microwave field strength and absorption uniformity across thesample within the microfluidic cell 420. In a manner analogous to thatfor the excitation elements 500, various configurations, layouts, ordesigns are possible for the microwave substrate's conductive traces610. FIG. 10G includes image depicting multiple representative types ofmicrowave substrate conductive trace layouts in accordance withparticular embodiments of the present disclosure.

Representative electric field simulation results corresponding todifferent coverslip excitation element layouts and microwave substrateconductive trace layouts are shown in FIGS. 10H and 10I. Such simulationcan facilitate the optimization of the energy deposition and uniformity,while maintaining large electrode free regions for sample observation.As indicated in FIG. 10I, the phase of the microwaves can be shiftedbetween alternating pulses to generate a vortex field pattern to expandthe microwave energy distribution more uniformly across the sample. InFIG. 10I, the E-field distribution for a half cycle is confined near theexcitation elements 500, where the sample is not visible optically. InFIG. 10I(1), there is no phase difference between port 1 and 2 (e.g. apush-push field); In FIG. 10I(2), the E-field distribution is for halfcycle when there is 180 degree phase difference between port 1 and 2(e.g. push-pull). Rotation of the phase in (2) between alternatingpulses delivers a more uniform time-averaged energy distribution.

FIGS. 11A-11D are block diagrams showing aspects of a design formicrowave signal generation and delivery circuitry in accordance withparticular embodiments of the present disclosure, such as themicrostrip-based capsule assembly 400 of FIGS. 9A-10E. In FIG. 11A, apulsed microwave source (e.g., an Anritsu MG3694C, Anritsu ElectricCorporation, Kanagawa, JP) provides pulsed microwave signals and allowsflexible control of a pulse train, frequency, and amplitude. A travelingwave tube (TWT) amplifier has high headroom for reliable operation, anda suppression grid at its output that allows thermal amplifier noise tobe eliminated during steady off state periods. Circulators with dummyloads protect devices from reflected power caused by circuit mismatches.The power divider separates the pulsed microwave signal into two feeds,and a phase shifter is used to control the relative phase between feeds.The darkened lines in FIG. 11A indicate phase stable connections/signalsat latter portions of the circuit. Fixed microwave manipulation elementsinclude matching networks, and further features on a dielectricsubstrate (e.g., PCB) side. Such elements can include baluns, Wilkinsonpower dividers, matching elements, phase shifters, or other types ofelements.

In FIG. 11B, an alternative topology is considered, having differentmicrowave sources and separate external pulse modulation. Multiple lowcost amplifiers can be used instead of a single TWT amplifier. Tunablematching is also shown. A low cost continuous wave microwave source isused in this embodiment instead of a complex signal generator, whichnecessitates independent pulse modulation. A fast switching PIN switchcan be used, for example, to achieve desired or required pulsemodulation. A low level signal is split by way of a power divider, andseparate low cost amplifiers amplify each channel separately. Multiplelow power amplifiers can be used to achieve higher total power output,in a manner readily understood by one of ordinary skill in the relevantart.

Impedance mismatches can arise from inaccuracies in construction orchanges in environmental factors. The right side portion of FIG. 11Bindicates how a directional coupler and a tunable matching network canbe used to achieve dynamic impedance matching. The directional couplerre-routes reverse power signals that are indicative of an impedancemismatch. By using a diagnostic tool, the impedance mismatch can beestimated and compensated for by adjusting the tunable matching network.Finally, a tuning process can be automated, such that dynamic matchingcan be performed in real time to compensate for impedance changes whenultra-fast freezing is carried out. The signal is fed to the dielectricsubstrate/PCB side, where additional microwave circuit elements canexist in a manner understood by one of ordinary skill in the relevantart.

FIG. 11C is a circuit schematic diagram illustrating a representativemanner of providing two signals to dual ports of a PCB board; and FIG.11D is a circuit schematic diagram illustrating representative aspectsof phase calibration between dual ports of a PCB circuit.

FIG. 11E is an image showing portions of a representative prototypesample preparation or fixation system 10 in accordance with anembodiment of the present disclosure. In an embodiment, the prototypesystem 10 utilizes a TWT amplifier that provides controlled excitationof specimens with microwave pulses as short as 100 nanoseconds tomicroseconds, for durations up to hundreds of milliseconds (or evencontinuous wave (CW)) while allowing access to power levels up to nearly1 kW. A representative TWT was specified to operate over both ISM bands,2.45 GHz and 5.8 GHz with a power at the fundamental frequency of atleast 500 Watts. The microwave pulses can be controlled with nearlyarbitrary pulse width, delay between pulses, and pulse amplitude; andall of these parameters can be altered during a single freezing event,so that the microwave energy can be matched precisely to the freezingfront as it propagates through the sample.

The TWT has the advantage that it can provide high power over a broadfrequency range. For pulses 100 nsec in duration (or less) the inputsignal must be modulated, either at the signal generator or with a PINdiode switch in series with the signal generator output. The design ofthe prototype system 10 enables a PIN fast modulation scheme, which issynchronized with a TWT suppression grid to eliminate the thermal noiseprior to the experiment. The suppression grid is turned off immediatelyprior to freezing, and a computer controlled high power microwave pulsetrain is triggered to correspond with the actuation of a cryogeniccoolant jet 220. Other embodiments in accordance with the presentdisclosure can utilize solid state microwave amplifiers instead of aTWT, in a manner understood by those of ordinary skill in the relevantart.

In various embodiments, the cryo-coolant jet 220 can be provided to theunderside of the thermal energy transfer substrate 112 by way of acommercially available cryo-condenser. FIGS. 12A and 12B are images of aparticular type of commercially available cryo-condenser suitable forproviding a cryo-coolant jet 220 in accordance with an embodiment of thepresent disclosure.

FIGS. 13A-13I are schematic illustrations of representative types ofmicrowave pulse sequences that can be provided in accordance withparticular embodiments of the present disclosure. One or more pulsecharacteristics or parameters (e.g., pulse amplitude, inter-pulseinterval, individual pulse duration, and/or other parameters) can beadjusted or dynamically changed or varied (e.g., in a selectable orprogrammable manner) during the provision, delivery, or application of amicrowave pulse sequence or train. Some embodiments include or utilize achirped pulse sequence, where a chirp pattern can dynamicallyaccommodate impedance mismatch associated with impedance changes orvariation resulting from rapid cooling of a capsule 110 and/or thesample(s), specimen(s), or fluid medium or media carried thereby. One ormore “chirp recipes” can be determined (e.g., based upon experimental orsimulated results) for particular sample types and/or volumes, where agiven chip recipe corresponds or gives rise to desired, intended, ortarget sample vitrification properties or results.

In addition to the foregoing, multiple embodiments in accordance withthe present disclosure avoid or substantially avoid thermal cooling ofoptical elements 55 such as a microscope objective, for instance, by wayof application (e.g., selective delivery) of a gas (e.g., a roomtemperature or slightly heated dry gas such as Nitrogen or compresseddry air). In embodiments that include an immersion lens, which involve afluid layer (e.g., a refractive index matching fluid) between amicroscope objective and the capsule's cover 114, a selectively orprogrammably activated gas jet (e.g., a dry gas such as Nitrogen, whichcan be heated) can be directed toward or to the fluid layer atparticular times, such as the onset of rapid cooling.

Aspects of particular embodiments of the present disclosure address atleast one aspect, problem, limitation, and/or disadvantage associatedwith exiting sample preparation, fixation, or vitrification techniques.While features, aspects, and/or advantages associated with certainembodiments have been described in the disclosure, other embodiments mayalso exhibit such features, aspects, and/or advantages, and not allembodiments need necessarily exhibit such features, aspects, and/oradvantages to fall within the scope of the disclosure. It will beappreciated by a person of ordinary skill in the art that several of theabove-disclosed systems, components, processes, or alternatives thereof,may be desirably combined into other different systems, components,processes, and/or applications. In addition, various modifications,alterations, and/or improvements may be made to various embodiments thatare disclosed by a person of ordinary skill in the art within the scopeand spirit of the present disclosure.

For example, a number of embodiments in accordance with the presentdisclosure need not be designed or suitable for microwave assistedcryo-fixation of samples, but can rather be designed for microwaveassisted chemical fixation of samples. At least some of such embodimentscan provide a support member other than a very high or extremely highthermal conductivity substrate 112 (e.g., a diamond or sapphire disk)on, as, or in very close proximity to a bottom surface of a sample cell402. Microwave assisted chemical fixation embodiments can includemicrofluidic elements such as those described above to facilitate theintroduction or circulation of one or more types of fluids (e.g.,liquids or gases) such as chemical substances in a chamber 116, andhence the exposure of a sample carried thereby to one or more of suchfluids.

As another example, certain embodiments in accordance with the presentdisclosure can include one or more groups or arrays of microfluidicmicrowave delivery chamber modules or sample cells 402 (e.g., a 2×2,3×3, 4×4, or larger array of sample cells 402). Depending uponembodiment details, only one, a small number, or possibly none of thecompartment interiors provided by the sample cells 402 can be configuredfor optical imaging at any given time (e.g., by way of selectivedisplacement or positioning of a set of microscope objectives relativeto individual sample cells 402 within the group or array of sample cells402); or multiple or all compartment interiors of the sample cells 402within the group or array of sample cells 402 can be configured forsimultaneous optical imaging, such as by way of fiber optic bundles,optical lens assemblies, and image capture devices corresponding to eachsample cell 402. In a sample cell group or array arrangement, microwaveassisted cryo-fixation and/or microwave assisted chemical fixation canoccur in a time sequenced or synchronized (e.g., essentiallysimultaneous) manner across multiple sample cells 402 within the groupor array of sample cells 402, for instance, based upon or in response toone or more trigger events. Following fixation, individual sample cells402 within the sample cell group or array can be transferred to one ormore particular destinations, for instance, a cryo-destinations such asa dewar containing LN, or a high resolution cryo-microscopy system(e.g., an SEM or a SHIM). Alternatively, in certain embodiments, anentire group or array of sample cells 402 can be transferred to apredetermined destination, such as a dewar containing LN.

The preceding and other embodiments and embodiment variations areencompassed by the present disclosure, which is limited only by thefollowing claims.

1. A system for preparing or fixing a biological sample, the systemcomprising: a sample capsule structure comprising: a compartmentproviding an internal volume in which the sample can be carried, and inwhich the sample is exposed to or carried by a fluid; and a microwaveapplicator comprising a set of microwave signal delivery elementsconfigured for exposing the sample within the compartment to microwaveradiation while the sample is exposed to the fluid.
 2. The system ofclaim 1, wherein the sample capsule is configured to facilitate at leastone of microwave assisted chemical sample fixation and microwaveassisted cryogenic sample fixation.
 3. The system of claim 1, whereinthe microwave radiation is provided at a frequency of betweenapproximately 2 GHz and approximately 18 GHz.
 4. The system of claim 3,wherein the microwave radiation is provided at a frequency ofapproximately 2.45 GHz, 5.8 GHz, 10 GHz, or a combination thereof. 5.The system of claim 1, wherein the microwave radiation is provided byway of pulsed microwave signals having a high peak or instantaneouspower and a low average power.
 6. The system of claim 1, wherein thecompartment and the microwave applicator are carried or supported by adielectric substrate that carries conductive traces configured forproviding microwave signals to the microwave applicator.
 7. The systemof claim 6, wherein the dielectric substrate additionally carries atleast one of a set of microwave functional elements and a set ofmicrowave coupler elements that are electrically couplable to themicrowave applicator.
 8. The system of claim 7, wherein (a) the set ofmicrowave functional elements includes at least one of matching devices,a balun, a set of phase shifters, a set of power dividers, a set ofisolators, a set of microwave opens, a set of microwave shorts, a set ofmicrowave gaps, a set of microwave slots, a set of vias, a set ofcouplers couplers, a set of controlled length and controlled impedancetransmission line elements, a set of microwave resistors, a set ofmicrowave capacitors, and a set of inductors, and (b) the set ofmicrowave coupler elements includes at least one of metal contactelements and associated mechanical pressure or force application devicesthat establish electrical signal communication between metal-to-metalcontacts, intermediate conductive film(s) between metal-to-metalcontacts, gap feeds, and gap couplers.
 9. The system of claim 1, whereinthe sample capsule structure is shaped and dimensioned to at leastsubstantially match the size of a standard optical microscopy slide. 10.The system of claim 9, wherein the sample capsule structure is shapedand dimensioned for integration into an optical microscope stage orplatform structure.
 11. The system of claim 1, wherein the microwaveapplicator comprises a support member that is shaped and dimensioned toat least substantially match the size of an optical microscopy slidecoverslip, and wherein the support member carries a patterned set ofexcitation elements that serve as electrodes by which microwave energycan be provided to internal portions of the compartment.
 12. The systemof claim 2, wherein the sample capsule further comprises a thermalenergy transfer substrate providing at least a very high thermalconductivity, the thermal energy transfer substrate disposed beneath thesample and having a bottom face to which a cryogenic coolant jet can bedirected to jet freeze the sample extremely rapidly while the microwaveapplicator exposes the sample within the compartment to microwaveradiation.
 13. The system of claim 12, wherein the sample capsuleincludes at least one freeze fracture initiation element configured forfacilitating in-situ freeze fracturing of the sample.
 14. The system ofclaim 12, wherein the microwave applicator is disposed above the sample.15. The system of claim 12, wherein the thermal energy transfersubstrate comprises diamond or sapphire.
 16. The system of claim 12,wherein top face of the thermal energy transfer substrate forms a bottomsurface of the interior of the sample capsule, on which the sample canbe grown or placed.
 17. The system of claim 13, wherein the systemfurther comprises a cryogenic cooling unit configured for supplying thecryogenic coolant jet and directing the cryogenic coolant jet to abottom face of the thermal energy transfer substrate that is below thesample, such that the sample is flash frozen by way of extremely rapidtransfer of thermal energy through the thermal energy transfer substrateto the cryogenic coolant jet.
 18. The system of claim 17, wherein themicrowave radiation is provided in a manner that disrupts water moleculepentamer cluster formation to vitrify portions of the sample duringultra-rapid freezing.
 19. The system of claim 18, wherein the microwaveradiation is provided in a manner that results in a vitrification depthwithin the compartment of up to approximately tens of microns.
 20. Thesystem of claim 1, wherein the sample capsule structure furthercomprises a set of microfluidic elements configured for introducing thefluid into and withdrawing the fluid out of the compartment.
 21. Thesystem of claim 20, wherein the set of microfluidic elements includes aninternal laminar flow region that forms at least portions of theinternal volume of the compartment, and across which fluid flow to whichthe sample is exposed can occur in at least an approximately laminarmanner.
 22. The system of claim 21, wherein the sample capsule structurecomprises a molded microfluidic cell that includes the set ofmicrofluidic elements.
 23. The system of claim 1, further comprising anoptical imaging system configured for receiving or capturing an image ofthe sample within the compartment.
 24. The system of claim 23, whereinthe optical imaging system is configured for receiving or capturing animage of the sample within the compartment while the sample is exposedto the fluid and/or while the sample is exposed to the microwaveradiation.
 25. The system of claim 23, wherein the optical imagingsystem comprises a set of optical microscope objective lenses and anoptical microscope platform configured for supporting the sample capsulestructure such that an objective lens within the set of objective lensescan focus on a portion of the sample within the compartment.
 26. Thesystem of claim 1, wherein the sample capsule structure includes atleast one set of fiducial markers to facilitate correlative microscopyprocedures.
 27. The system of claim 26, wherein the sample capsulestructure includes a first set of fiducial markers internal to thecompartment and a second set of fiducial markers external to thecompartment.
 28. The system of claim 1, wherein the system comprisesmultiple sample capsule structures, each of which is configured forexposing a distinct sample to a fluid simultaneous with exposing thesample to microwave radiation.
 29. The system of claim 28, wherein eachof the multiple sample capsule structures is configured to facilitate atleast one of microwave assisted chemical sample fixation and microwaveassisted cryogenic sample fixation.
 30. A method for preparing or fixinga sample by way of ultra-rapid freezing, comprising: providing a samplecapsule structure that includes a compartment having an internal volumein which the sample can be carried, and in which the sample is exposedto or carried by a fluid; and exposing the sample capsule to a cryogeniccoolant jet while simultaneously exposing the sample capsule to pulsedmicrowave radiation in a manner that disrupts initial ice crystalnucleation events within the compartment within tens of microseconds tothereby provide a vitrification depth within the compartment of at leastapproximately tens of microns.
 31. The method of claim 30, wherein thepulsed microwave radiation exhibits a high peak or instantaneousintensity, and wherein the pulsed microwave radiation exhibits a lowaverage intensity.
 32. The method of claim 30, wherein the sample iscarried between an upper surface of the compartment and a lower surfaceof the compartment, and wherein the cryogenic coolant jet is configuredto cool the lower surface of the compartment extremely rapidly, and thepulsed microwave radiation is provided above or from the upper surfaceof the compartment.
 33. The method of claim 30, further comprisingpassing the fluid through the compartment by way of a set ofmicrofluidic elements.
 34. The method of claim 30, further comprising:providing at least one set of fiducial markers carried by the samplecapsule structure; and determining a set of spatial positionscorresponding to particular portions of the sample relative to the atleast one set of fiducial markers.
 35. The method of claim 30, furthercomprising freeze fracturing the sample while the sample is carriedwithin the compartment.